US11799296B2 - Islanding detection system and method - Google Patents

Islanding detection system and method Download PDF

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US11799296B2
US11799296B2 US17/453,866 US202117453866A US11799296B2 US 11799296 B2 US11799296 B2 US 11799296B2 US 202117453866 A US202117453866 A US 202117453866A US 11799296 B2 US11799296 B2 US 11799296B2
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inverter
islanding detection
islanding
detection
mode
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US20220190604A1 (en
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Shen Chen
Feidong XU
Xuancai ZHU
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Delta Electronics Shanghai Co Ltd
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Delta Electronics Shanghai Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/381—Dispersed generators
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/25—Arrangements for measuring currents or voltages or for indicating presence or sign thereof using digital measurement techniques
    • G01R19/2513—Arrangements for monitoring electric power systems, e.g. power lines or loads; Logging
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for feeding a single network from two or more generators or sources in parallel; Arrangements for feeding already energised networks from additional generators or sources in parallel
    • H02J3/388—Arrangements for the handling of islanding, e.g. for disconnection or for avoiding the disconnection of power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2101/00—Supply or distribution of decentralised, dispersed or local electric power generation
    • H02J2101/20—Dispersed power generation using renewable energy sources
    • H02J2101/22—Solar energy
    • H02J2101/24—Photovoltaics
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2103/00—Details of circuit arrangements for mains or AC distribution networks
    • H02J2103/30—Simulating, planning, modelling, reliability check or computer assisted design [CAD] of electric power networks
    • H02J2300/24—
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

  • the application relates to islanding detection, and particularly to an islanding detection system and method for multiple inverters operating in parallel.
  • inverter In a new energy power generation system, inverter is often used to convert DC electric energy into AC electric energy, and output of the inverter is connected to a load and a grid through a breaker.
  • the inverter and the local load When the grid is disconnected due to a fault or other reasons, the inverter and the local load will operate in an islanding state. Since the islanding state will threaten overhaul and maintenance, it shall be detected and terminated in some conditions.
  • detection of the islanding operation state comprises active islanding detection and passive islanding detection.
  • the passive islanding detection is realized by monitoring parameters such as voltage and frequency at PCC point.
  • the passive islanding detection since the passive islanding detection always has a large non-detection zone (NDZ), the active islanding detection shall be adopted as a supplement.
  • the active islanding detection comprises active frequency shift, reactive injection, harmonic injection, and the like.
  • a common processing measure is to adopt same islanding detection method and synchronous injection method. That is, in a system where multiple inverters are connected in parallel, the same active islanding detection method is adopted for all inverters.
  • a master controller shall be designed in the system.
  • the master controller can be a separate controller; or the master controller may be a controller of one inverter with controllers of other inverters as slave.
  • the connection between the master controller and the slave controllers is established through communication.
  • the master controller outputs a synchronous reference signal and transmits the synchronous reference signal to the respective slave controllers. After receiving the synchronous signal, the slave controllers execute the islanding detection action.
  • a high-speed communication bus such as a CAN bus
  • a high-speed communication bus such as a CAN bus
  • the premise of the processing measure is that each inverter adopts the same islanding detection mode, and high-speed (or real-time) communication needs to be established between inverters to realize accurate synchronization. If one inverter in the system adopts different mode or the inverters in the system are not synchronized, islanding detection of the system may be failed, resulting in poor robustness of the algorithm.
  • one object of the application is to provide an islanding detection system for multiple inverters operating in parallel.
  • a current detection circuit on a grid side or an AC side of the second inverter it can perform distributed or centralized islanding detection for different situations adaptively, thereby improving the pass rate of islanding detection.
  • the application provides an islanding detection system for multiple inverters operating in parallel, the multiple inverters at least comprising a first inverter and a second inverter connected in parallel, wherein the islanding detection system comprises:
  • the application further provides an islanding detection method for multiple inverters connected in parallel, the multiple inverters at least comprising a first inverter and a second inverter connected in parallel, wherein the islanding detection method comprises:
  • FIG. 1 is a circuit diagram of an islanding detection system for multiple inverters operating in parallel according to one embodiment of the application.
  • FIG. 2 is a simplified circuit diagram of an islanding detection system for multiple inverters operating in parallel according to another embodiment of the application.
  • FIG. 3 is islanding detection mode based on reactive current injection according to one embodiment of the application.
  • FIG. 4 is a flow diagram of an islanding detection method for multiple inverters operating in parallel according to one embodiment of the application.
  • FIG. 5 is a flow diagram of centralized islanding detection according to one embodiment of the application.
  • FIG. 6 is a flow diagram of distributed islanding detection according to one embodiment of the application.
  • FIG. 7 is a schematic diagram of distributed islanding detection mode based on a synchronous injection mode according to one embodiment of the application.
  • FIG. 8 is a schematic diagram of distributed islanding detection mode based on a time-division injection mode according to one embodiment of the application.
  • FIG. 9 is a flow diagram of distributed islanding detection according to another embodiment of the application.
  • FIG. 10 is a schematic diagram of distributed islanding detection mode based on an adversarial injection mode according to one embodiment of the application.
  • an islanding detection system for multiple inverters operating in parallel comprises at least a first inverter 131 and a second inverter 170 connected in parallel.
  • the islanding detection system further comprises a current detection circuit 140 (which is referred to as a first current detection circuit) and a controller 132 .
  • the first current detection circuit 140 may be arranged on a grid side or an AC side of the second inverter 170 .
  • the controller 132 is connected to the first current detection circuit 140 and the first inverter 131 , and determines whether to perform a distributed islanding detection or a centralized islanding detection on the first inverter 131 and the second inverter 170 according to a grid voltage signal obtained by sampling a grid voltage and a current detection signal detected by the first current detection circuit 140 .
  • FIG. 1 illustrates a circuit diagram of an islanding detection system for multiple inverters operating in parallel according to one embodiment of the application.
  • the system may comprise: a first DC source 110 , a second DC source 120 , an inverter system 130 , a local load 190 , a grid 150 , a third DC source 160 , a second inverter 170 , a first current detection circuit 140 and a connector 180 .
  • the first DC source 110 for example, a photovoltaic panel, is connected to a first inverter 131 .
  • the second DC source 120 for example, a household energy storage battery, is connected to the first inverter 131 .
  • the inverter system 130 is an energy storage inverter system.
  • the third DC source 160 for example, an on-board battery, is connected to the second inverter 170 .
  • the second inverter 170 is an on-board charger, for example.
  • the connector 180 may be a connector in form of a charging gun or the like.
  • the system includes an electric vehicle, a photovoltaic panel, an energy storage battery, and an energy storage inverter.
  • the first DC source 110 is the photovoltaic panel
  • the second DC source 120 is the energy storage battery
  • the third DC source is power battery installed in the electric vehicle
  • the first inverter 131 is the energy storage inverter
  • the second inverter 170 is a bi-directional charger installed in the electric vehicle
  • the connector 180 is a charging gun integrated into the energy storage inverter.
  • the energy storage inverter is designed with an energy management system that can perform state monitoring and power control on the energy storage battery and the power battery in the electric vehicle. It shall be noted that the respective DC sources and the inverters may also be applied to other technical fields, but the application is not limited thereto.
  • the inverter system 130 may comprise a first inverter 131 , a controller 132 , a current detection circuit 133 (which is referred to as a second current detection circuit), and a breaker 134 .
  • the first inverter 131 , the controller 132 , the second current detection circuit 133 , and the breaker 134 shown in FIG. 1 are discrete components, and in other embodiments, the controller 132 , the second current detection circuit 133 , and the breaker 134 may be integrated into the first inverter 131 . It shall be noted that the inverter system 130 shall be provided with one second current detection circuit 133 in order to achieve control and islanding detection, which is arranged on an AC side of the first inverter 131 .
  • the second current detection circuit 133 is desired by the inverter system 130 itself and exists in current hardware, so explanations are omitted here.
  • the first current detection circuit 140 shall be additionally provided in the system.
  • the first current detection circuit 140 is arranged on an output side of the second inverter 170 , for example, before and after the connector 180 .
  • the first current detection circuit 140 is arranged on a common output side of the first inverter 131 and the second inverter 170 , i.e., a grid side.
  • the second current detection circuit 133 and the first current detection circuit 140 may be current sensors CT, and a current detection signal sampled by the current sensors CT is inputted into the controller 132 .
  • the inverter system 130 comprises a voltage detection circuit (not shown) for sampling a grid voltage and inputting a grid voltage signal into the controller.
  • the controller 132 completes recognition of islanding detection mode of the second inverter 170 and/or adjustment of islanding detection mode of the first inverter 131 itself through the processing of the sampled signals (e.g., the current detection signal and the grid voltage signal).
  • the controller 132 is electrically connected to the first inverter 131 and transmits a control signal to the first inverter 131 , thereby controlling the normal operational state of the first inverter 131 , and realizing islanding detection and subsequent actions of the first inverter 131 .
  • the controller 132 controls the breaker 134 simultaneously, and after islanding is detected, the controller 132 controls the breaker 134 to disconnect the connection between the inverter system 130 and the load 190 .
  • FIG. 2 illustrates a simplified circuit diagram of an islanding detection system for multiple inverters operating in parallel in FIG. 1 of the application.
  • the first current detection circuit 140 is arranged at an output of the second inverter 170 .
  • the first current detection circuit 140 may also be arranged on the grid side, with identical function and effect.
  • FIG. 3 illustrates islanding detection mode based on reactive current injection according to one embodiment of the application.
  • the functional mechanism of the islanding detection mode based on reactive current injection is as follows:
  • Step 1 injecting a reactive current Iq periodically on an output side of the inverter
  • Step 2 calculating an output frequency according to a grid voltage signal, entering into an enhanced injection mode to increase the injection intensity of the reactive current when the output frequency changes, stopping injection and observing the output frequency after the injection intensity is increased to a certain value;
  • Step 3 recording one event when the output frequency observed in step 2 follows the frequency curve shown in FIG. 3 ;
  • Step 4 determining the occurrence of islanding when the event in FIG. 3 is detected several times continuously.
  • the islanding detection mode includes but is not limited to the reactive current injection manner, and may also be other manners.
  • the islanding detection when the multiple inverters operate in parallel is described by taking the reactive current injection as an example.
  • FIG. 4 illustrates a flow diagram of an islanding detection method for multiple inverters operating in parallel according to one embodiment of the application. As shown in FIG. 4 , the method mainly comprises:
  • Step S 10 sampling a grid voltage to obtain a grid voltage signal, and sampling a current on a grid side or on an AC side of the second inverter to obtain a current detection signal;
  • Step S 20 fitting islanding detection mode of the second inverter according to the current detection signal and the grid voltage signal;
  • Step S 30 judging whether the islanding detection mode is matched with one of islanding detection modes library.
  • the current detection signal sampled by the first current detection circuit 140 and the grid voltage signal sampled by a voltage detection circuit are inputted into the controller 132 .
  • the controller 132 fits the islanding detection mode of the second inverter 170 according to the current detection signal and the grid voltage signal. Specifically, the controller 132 may obtain electrical parameters including information of voltage, current, active power, reactive power, and frequency of the second inverter 170 according to the sampled signals.
  • the controller 132 completes analysis and extraction of key features of the islanding detection mode of the second inverter 170 , including disruption types (e.g., frequency shift, reactive injection, harmonic injection, etc.), disturbed period, disturbed amplitude, and the like, by obtaining mass electrical parameters of the second inverter 170 .
  • disruption types e.g., frequency shift, reactive injection, harmonic injection, etc.
  • the controller 132 fits the islanding detection mode of the second inverter 170 according to the extracted features. Fitting of the islanding detection mode of the second inverter 170 may be based on mass sampled data (e.g., mass historical sampled data) including the current detection signal and the grid voltage signal sampled in the current period. As for fitting of the islanding detection mode of the second inverter 170 , the fitting method in the prior art, or the method of machine learning may be adopted, but the application is not limited thereto.
  • the controller 132 performs distributed islanding detection or centralized islanding detection accordingly according to judging whether the islanding detection mode is matched with one of the islanding detection modes library.
  • the controller 132 is stored with a library including several typical islanding detection modes.
  • the controller 132 compares the fitted islanding detection mode of the second inverter 170 with the mode in the library. If the fitted islanding detection mode overlaps with one mode with a certain ratio, the matching is successful, otherwise, the matching is failed.
  • step S 40 is performed; if the matching is successful, step S 50 is performed.
  • Step S 40 performing centralized islanding detection.
  • Step S 50 performing distributed islanding detection.
  • the distributed islanding detection is performed, wherein the first inverter 131 and the second inverter 170 connected in parallel each performs islanding detection separately.
  • the centralized islanding detection is performed, wherein the first inverter 131 and the second inverter 170 serve as an integral body and the centralized islanding detection is performed by the first inverter 131 .
  • the controller 132 compensates a control signal for detecting an islanding operational state of the first inverter 131 in real time according to the current detection signal, i.e., compensates an islanding detection control signal of the first inverter 131 in real time, and outputs the compensated islanding detection control signal to the first inverter 131 .
  • FIG. 5 is a flow diagram of centralized islanding detection according to one embodiment of the application, comprising steps of:
  • Step S 401 obtaining parameters of the second inverter according to a grid voltage signal and a current detection signal.
  • the controller 132 may obtain parameters of the second inverter 170 , including information of voltage, current, active power, reactive power, frequency, or harmonic wave according to the current detection signal and the grid voltage signal obtained by sampling.
  • Step S 402 judging whether the second inverter performs islanding detection, if yes, performing step S 403 , otherwise, performing step S 404 ;
  • Step S 403 calculating compensation for an islanding detection control signal of the first inverter according to parameters of the islanding detection mode of the second inverter;
  • Step S 404 updating the islanding detection control signal of the first inverter.
  • the islanding detection control signal to be injected to the first inverter 131 is a reactive current 1 A, for example. Accordingly, a judging result of step S 402 is “yes”, i.e., the second inverter 170 is performing islanding detection. Meanwhile, for example, if it is calculated that the second inverter 170 is injected with a reactive current of 0.5 A according to the sampled signals, a compensation of an islanding detection control signal of the first inverter is calculated accordingly and its value is ⁇ 0.5 A.
  • the first inverter 131 performs islanding detection according to the updated islanding detection control signal.
  • the second inverter 170 is injected with a reactive current of ⁇ 0.5 A
  • the value of the compensation of the islanding detection control signal of the first inverter is 0.5 A
  • the reactive current is not limited to the electrical parameters and may be an injected harmonic wave, for example. If a judging result of step S 402 is “no”, the first inverter may update the control signal according to its islanding detection mode.
  • FIG. 6 is a flow diagram of distributed islanding detection according to one embodiment of the application. As shown in FIG. 6 , it comprises:
  • Step S 501 loading parameters of islanding detection mode of the second inverter
  • Step S 502 configuring islanding detection mode of the first inverter to be the same as that of the second inverter;
  • Step S 503 judging whether detection shall be synchronized
  • step S 504 is performed, and if no, step S 505 is performed;
  • Step S 504 adopting synchronous injection mode
  • Step S 505 adopting time-division injection mode.
  • the controller 132 loads parameters of the islanding detection mode of the second inverter 170 , including information of disruption types, injection period, injection amplitude, and the like.
  • the controller 132 configures the first inverter 131 to adopt the same islanding detection mode as the second inverter 170 , and controls an islanding detection control signal of the first inverter 131 to be synchronous or asynchronous in timing with the second inverter 170 .
  • FIG. 7 illustrates a schematic diagram of islanding detection modes of different inverters based on a synchronous injection mode.
  • reactive current injection referring to the fitted islanding detection mode of the second inverter 170 in FIG. 7 , if an injected reactive current is shown by a second inverter Iq in FIG. 7 and a frequency change when islanding occurs is shown by a second inverter f in FIG. 7 , the first inverter 131 is configured to load the same islanding detection mode as the second inverter 170 and injects a reactive current periodically.
  • An injection time of reactive current of the first convert 131 is synchronous with that of the second inverter 170 , and an injection amplitude of reactive current of the first convert 131 is consistent with that of the second inverter 170 .
  • An object of the design is to make injection signals of the two inverters form a superimposed effect and improve the speed of the islanding detection.
  • the first inverter adopts the same islanding detection mode as the second inverter, but the islanding detection control signal of the first inverter is alternated strictly in timing with that of the second inverter, thereby ensuring no mutual effect of islanding detection there between.
  • FIG. 8 illustrates a schematic diagram of islanding detection modes of different inverters based on a time-division injection mode.
  • reactive injection refer to an islanding detection mode of the second inverter 170 in FIG. 8 , i.e., the injected reactive current is shown by a second inverter Iq in FIG. 8 , and a frequency change when islanding occurs is shown by a second inverter f in FIG. 8 .
  • the first inverter 131 is configured to load the same islanding detection mode as the second inverter 170 by the controller 132 and injects the reactive current periodically.
  • the injection action of the first convert 131 in each period is completed within an undisturbed interval of the second inverter 170 .
  • An object of the design is to make two converters perform independently islanding detection without interference with each other.
  • an adversarial injection mode may be adopted.
  • the specific flow diagram, as shown in FIG. 9 comprises:
  • Step S 701 obtaining parameters of islanding detection mode of the second inverter
  • Step S 702 configuring the islanding detection mode of the first inverter to be symmetrical with that of the second inverter;
  • Step S 703 adopting adversarial injection mode.
  • the first inverter 131 is configured to adopt an islanding detection mode which is symmetrical with the islanding detection mode of the second inverter to represent an adversarial relationship where one decreases while the other increases. Moreover, a detection period and time of the first inverter 131 are synchronous with those of the second inverter 170 , such that a sum of the control signals of them is constant.
  • FIG. 10 illustrates a schematic diagram of islanding detection modes of different inverters in a synchronous injection mode.
  • reactive current injection referring to the fitted islanding detection mode of the second inverter 170 in FIG. 10 , if an injected reactive current is shown by a second inverter Iq in FIG. 10 and a frequency change when islanding occurs is shown by a second inverter f in FIG. 10 , the first inverter 131 is configured to load an islanding detection mode which is symmetrical to that of the second inverter 170 by the controller 132 , and the first inverter 131 is also injected with the reactive current periodically.
  • An injection time of the reactive current of the first converter 131 is synchronous with that of the second inverter 170 , and an injection amplitude of the reactive current of the first converter 131 form an adversarial mode with that of the second inverter 170 , to keep the total reactive current injection constant. That is, the injection amplitude of the reactive current of the first inverter 131 is configured to decrease as the injection amplitude of the reactive current of the second inverter 170 increases.
  • An object of the design is to make injection signals of the two inverters form a superimposed effect and improve the speed of islanding detection, while the total reactive current injection may be controlled.
  • one injection mode of synchronous injection mode, time-division injection mode, and adversarial injection mode may be selected according to needs.
  • the controller 132 configures the islanding detection mode of the first inverter 131 to be the same as that of the second inverter 170 , and the controller 132 applies an islanding detection control signal to the first inverter 131 in a synchronous injection mode or time-division injection mode relative to the second inverter 170 , i.e., the controller 132 applies an islanding detection control signal corresponding to the islanding detection mode to the first inverter 131 .
  • the controller 132 configures the islanding detection mode of the first inverter 131 to be symmetrical with that of the second inverter 170 , and the controller 132 applies an islanding detection control signal to the first inverter 131 in an adversarial injection mode relative to the second inverter 170 , i.e., the controller 132 applies an islanding detection control signal corresponding to the islanding detection mode to the first inverter 131 .
  • the controller recognizes the islanding detection mode of the second inverter, matches it with typical islanding detection mode preset in a library, and determines whether to perform a distributed or a centralized islanding detection according to the matching results, thereby improving a success rate of islanding detection.
  • the islanding detection system for the multiple inverters operating in parallel connection of the application is simple in structure, and it is unnecessary to establish a complicated communication network in real time and matching is simple.
  • the system of the application is suitable theoretically for any second inverter, and the second inverter does not have to make any change in design (including hardware and software).
  • the control signal for detecting an islanding operational state of the first inverter is compensated in real time, thereby reducing interference of islanding detection of the second inverter.
  • interference of islanding detection between different inverters is eliminated adopting the synchronous injection mode, time-division injection mode, or adversarial injection mode.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Inverter Devices (AREA)
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